Revert "fix(portal): detect changes for portal hostview while before attaching. (#4370)"

[jelbourn]

This reverts a change where attachComponentPortal in DomPortalHost would run detectChanges before attaching the embedded view to the view container.

This revert came about because it broke some datepicker features, but ultimately brought to light that having a call to detectChanges here prevents the user from initializing anything on the portal component before change detection runs, which means that any kind of one-time initialization will no longer work.

This also:

• Adds a test for the datepicker which would have caught this regression.
• Fixes the original snackbar issue (MdSnackbar enters the DOM already in view, preventing the correct animation. #4318) by calling detectChanges in the snackbar code

Fixes #5065

[kara]

LGTM

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